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PERPUSTAKAAN KU; TTHO
11111111111111111111111111111111111111111111111111111111111111111111111111111111 3 0000 00110182 7
Saya
PSZ 19: 16 (Pind. 1 97)
UNIVERSITI TEKNOLOGI l\lALA YSIA
BORANG PENGESAHAN STATUS TESIS·
JUDUL: A COMPARISON OF NUMERICAL METHODS FOR SOLVING THE BRATU AND BRATU-TYPE PROBLEMS
SESI PENGA.JIAN: 2004/2005
RUHAILA BINn MD. KASMANI (IIURUF BESAR)
mcngaku mcmbcnarkan tcsis (PSM-I Sarjana 1 GektBr-f<filsafah)* ini disimpan di Pcrpustakaan Univcrsiti Tcknologi Malaysia dcngan syarat-syarat kcgunaan scpcrti bcrikut:
I. Tcsis adalah hakmilik Univcrsiti Tcknologi Malaysia. 2. Pcrpustakaan Univcrsiti Tcknologi Malaysia dibcnarkan membuat salinan untuk
tujuan pengajian sahaja. 3. Pcrpustakaan dibenarkan mcmbuat salinan tesis ini scbagai bah an pcrtukaran antara
institusi pcngajian tinggi. 4. ** Sila tandakan (,j)
D SULIT
D TERHAD
CD TIDAK TERHAD
(TANDATANGAN PENULlS)
Alamat Tctap: 36, .lIn. Tcratai 4, Taman Bakri Indah, 84200 Bakri, 1\1uar, .Johor.
Tarikh: 16 Mac 2005
CA T A TAN * Potong yang tidak berkenaan .
(Mcngandungi maklumat yang bcrdarjah kcsclamatan atau kcpcntingan Malaysia scpcrti yang tcrmaktub di dalam AKTA RAHSIA RASMI 1972)
(Mcngandungi maklumat TERHAD yang tclah ditcntukan olch organisasifbadan di mana pcnyclidikan dijalankan)
Disahkan olch
(TANDATANGAN I'ENYELlA)
":\1 DR. ALI AIm. RAII:\L\:\ Nama Pcnyclia
Tarikh: 16 i\lac 2005
•• Jib tesis ini SULlT atau TERIIAD. sib lampirbn surat dJfipada plhak t>crkulSa./or"an''3si berkcnaan dengan mcnyatabn sekali scbab dan tcmpoh tcsis ini pcrlu dikclasbn sch"p' SULlT atau TERHAD .
• Tcsis dimaksudbn sebagai tcsis bagi Ijazah Doktor ralS3fah dan Sarpna SCc.1ra !"cmclidlbn. mau discrtai Dagi pcngajian sccara kcqa kursus dan penyclidibn. atau Laroran Pcold. Sorl"n" 1\luda (I'S1\1)
"I hereby declare that I have read this thesis and in my
opinion this thesis is sufficient in terms of scope and quality for the
award of the degree of Ivlaster of Science (Mathematics)"
Signat.ure '{~l ,oJ ~ 2_~! <-c· <'~,
C· .. · .. · .. ·(j'··············· .. ·····~········· .. ··
Name of Sup~rvisor Assoc. Prof. Dr. Ali Abd.Rahman
Date 16 Ivlarch 2005
A COIvIPARISOIi OF NUlvIERICAL IvIETHODS FOR SOLVING
THE BRATU AND BRATU-TYPE PROBLEMS
RUHAILA IvID.KASMANI
A dissertation submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Science UVlathematics)
Faculty of Science
Universiti Telmologi Malaysia
t-./IARCH 2005
11
I declare that this thesis entitled "A Comparison of Numerical
Methods for Solving the Bmtu and Bmtu-Type Problems" is the
result of my own research except as cited in the references. The
thesis has not been accepted for any degree and is not concurrently
submitted in candidature of any degree.
Signature
Name Ruhaila Md.Kasmani
Date 16 March 2005
III
Tp my beloved family and friends.
iv
ACKNOWLEDGEMENTS
In the name of Allah, The Most Gracious and The Ivlost ivIerciful. First
of all, thanks to Almight~r Allah for graciously bestowing me the perseverance to
tmdertake this study.
I would like to express my heartfelt gratitude to my supervisor, Associate
Professor Dr. Ali Abd.Rahman for his valuable advise and great encouragement
as well as for his excellent guidance and assistance for this dissertation.
A special thanks and a deepest appreciation to my beloved sister, Rafiziana
IVld.Kasmani for her cooperation and undivided support in completion of this
work. A warmest gratitude dedicates to my parents for their patience, prayers,
and encouragement thro~lghout my studies here in UTlvI .
Lastly, special thanks are extended to my friends for their cooperation and
assistance.
v
ABSTRACT
The Bratu problem ul/(x) + /\eu(x) = 0 with u(O) = u(l) = 0 has two
exact solutions for values of 0 < A < Ac, no solutions if A > Ac while unique
solution is obtained when A = Ac where Ac = 3.513830719 is the critical
value. The First Bratu-Type problem corresponds A = _7[2 while the Second
Bratu-Type problem is ul/(x) + 7[2e-u(x) = o. The exact solution of the First
Bratu-Type problem blows up at x = 0.5 while the Second Bratu-Type problem
is continuous. The present work seeks to compare various numerical methods
for solving the Bratu and Bratu-Type problems. The numerical methods are the
standard Adomian decomposition method, the modified Adomian decomposition
method, the shooting method and the finite difference method. These methods
are implemented using Maple. Convergence is achieved by applying the four
methods when 0 < A ::; 2, however the shooting method is the most effective
method as it gives the smallest maximum absolute error. ·When A = Ac, none of
these methods give the convergence solutions. Due to the nature of the solution
of the First Bratu-Type problem, only the shooting method and the modified
Adomian decomposition method can give the convergence values to the exact
solution. The finite difference method is proved to be the most effective method
for the Second Bratu-Type problem compared to other methods.
Keywords: Bratu problem, Bratu-Type problems, standard Adomian decomposi
tion method, modified Adomian decomposition method, shooting method, finite
difference method.
vi
ABSTRAK
Masalah Bratu UIl(X)+AeU(X) = 0 dengan syarat sempadan v.(O) = u(l) = 0
mempunyai dua penyelesaian bagi 0 < A < Ae , tiada penyelesaian jika /\ > /\
dan penyelesaian unik jika A = Ae di mana Ae = 3.513830719 adalah merupakan
nilai genting. rvIasalah Jenis-Bratu Pertama mengambil nilai A = _1[2 manakala
masalah .Ienis-Bratu Kedua adalah u"(x) + 1[2e-u (x) = O. Penyelesaian sebe
nar bagi masalah Jenis-Bratu Pertama meningkat secara mendadak pada titik
x = 0.5 manakala penyelesaian sebenar masalah Jenis-Bratu Kedua adalah selan
jar. Disertasi ini melaporkan mengenai perbandingan di antara beberapa kaedah
berangka bagi menyelesaikan masalah Bratu dan Jenis-Bratu. Perbandingan ini
melibatkan penggunaan empat kaedah iaitu kaedah penghuraian Adomian asal,
kaedah penghuraian Adomian terubahsuai, kaedah penembakan dan kaedah pem
beza terhingga. Setiap penyelesaian berangka dilaksanakan dengan menggunakan
Maple. Bagi kes 0 < A ::::; 2, keempat-empat kaedah tersebut telah memberikan
penyelesaian berangka yang menumpu. Didapati kaedah penembakan merupakan
kaedah yang paling efektif. Hanya kaedah penembakan dan kaedah penghuraian
Adomian terubahsuai telah menunjukkan penyelesaian menumpu bagi masalah
Jenis-Bratu Pertama. Kaedah pembeza terhingga merupakan kaedah yang pal
ing efektif bagi mendapatkan penyelesaian berangka untuk masalah Jenis-Bratu
Kedua berbanding kaedah yang lain.
Kata kunci: Masalah Bratu, masalah Jenis-Bratu, kaedah penghuraian Adomian
asal, kaedah penghuraian Adomian terubahsuai, kaedah penembakan, kaedah
pembeza terhingga.
CONTENTS
DEDICATION
ACKNOWLEDGETvlENTS
ABSTRACT
ABSTRAK
CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF APPENDICES
CHAPTER TITLE
1. INTRODUCTION
1.1 Ivlotivation
1.2
1.3
1.4
1.5
1.7
Problem Statement
Objectives
Scope of the Research
1.4.1 The Accuracy of the Solution
1.4.2 The Stability of the rdethod
Outline of Thesis
Concluding Remarks
\'11
III
iv
\'
vi
Vll
xi
xii
xiii
PAGE
15
IG
16
17
I::::
2.
3.
\'i i i
LITERATURE REVIE\V 19
2.1
2.2
2.3
Introduction
Analytical Solution of the Bratu Problem
Analytical solution of the First Bratu-Type
Problem
19
2.4 Analytical solution of the Second Bratu-Type
Problem
2.5
2.6
2 '7 .1
2.8
Adomian Decomposition rvlethod :20
Shooting Ivlethod 28
Finite Difference IVlethod :31
Concluding Remarks
METHODOLOGY :3:3
3.1
3.2
3.3
Introduction
Procedures of the IVlethods
3.2.1 The Procedure of the Adomian Decomposition
Ivlethod
33
3.2.2 The Procedure of the Shooting lvlethod :3Ci
3.2.3 The Procedure of the Finite Difference l\Ict.hod :r,
Analysis of Adomian Decomposition J\Jethod
3.3.1 The Standard Adomian Decomposition ~ Ie! hod ·12
3.3.2 The l\Iodified Adomian Decomposition ~Ict hod ·11
3.3.3 Application of the Standard Aclomian Dccolllpu:;it inn
l\Iethod to Solving the Brntu Problem ·!G
ix
3.3.4 Application of the Standard Adomian
Decomposition IVlethod to Solving the
First Bratu-Type Problem 51
3.3.5 Application of the Standard Adomian
Decomposition Method to Solving the
Second Bratu-Type Problem 56
3.3.6 Application of the Ivlodified Adomian
Decomposition Method to Solving the
Bratu Problem 59
3.3.7 Application of the Modified Adomian
Decomposition Method to Solving the
First Bratu-Type Problem 63
3.3.5 Application of the lVIodified Adomian
Decomposition Ivlethod to Solving the
Second Bratu-Type Problem 66
3.4 Analysis of the Shooting Method 70
3.4.1 Application of the Shooting IVIethod to
Solving the Bratu Problem 74
3.4·4 Application of the Shooting Method to
Solving the First Bratu-Type Problem 75
3.4.3 Application of the Shooting Ivlethod to
Solving the Second Bratu-Type Problem 77
3.5 Analysis of the Finite Difference l'vlethod 79
3.5.1 Application of the Finite Difference :Method to
Solving the Bratu Problem 83
3.5.2 Application of the Finite Difference Ivlethod to
Solving the First Bratu-Type Problem 85
3.5.3 Application of the Finite Difference lvlethod to
Solving the Second Bratu-Type Problem 88
3.6 Concluding Remarks 91
4.
4.1
4.2
4.3
4.4
4.5
4.6
5.
NUMERICAL RESULTS AND DISCUSSION
Introduction
Numerical Results of the Bratu Problem
Numerical Results of the First Bratu-Type Problem
Numerical Results of the Second Bratu-Type Problem
The Accuracy of the Solutions
4.5.1 The Bratu problem
4.5.2 The First Bratu-Type problem
4.5.3 The Second Bratu-Type problem
The Stability of the lvlethods
SUMMARY AND CONCLUSIONS
5.1
5.2
5.3
Summary
Conrlusions
Suggestions for Further \Vorks
REFERENCES
x
93
9:3
93
100
102
104
104
105
106
107
108
108
109
110
111
xi
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Corresponding values of e for various A ::; Ac 23
4.1 The upper solution of the shooting method
for the Bratu problem when A = 1 and A = 2 95
4.2 Comparispn between the exact solution (2.4) and the
four methods for A = 1 97
4.3 Comparison between the exact solution (2.4) and the
four methods for A = 2 99
4.4 The exact and numerical solutions of the
First Bratu-Type problem 101
4.5 The exact and numerical solutions of the
Second Bratu-Type problem 103
4.6 The accuracy of the Bratu problem 104
4.7 The accuracy of the First Bratu-Type problem 105
4.8 The accuracy of the Second Bratu-Type problem 106
XII
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Dependence of solutions of equation (2.5) upon A 21
2.2 The exact solution of the Bratu problem 24
2.3 The exact solution of the First Bratu-Type problem 25
2.4 The exact solution of the Second Bratu-Type problem 26
4.1 The upper and lower solutions of the Bratu problem 94
4.2 The upper solutions of the shooting method
for the Bratu problem when A = 1 and A = 2 95
4.3 The Bratu problem for A = 1 97
4.4 The Bratu problem when A = 2 99
4.5 The First Bratu-Type problem 101
4.6 The Second Bratu-Type problem 103
xiii
LIST OF APPENDICES
APPENDIX TITLE PAGE
A The outline of the Maple algorithm for the standard Adomian
decomposition method in solving the Bratu and Bratu-Type
problem 114
B The outline of the Maple algorithm for the modified Adomian
decomposition method in solving the Bratu and Bratu-Type
problem 115
C The outline of the IVlaple algorithm for the shooting method
in solving the Bratu and Bratu-Type problem 116
D The outline of the Maple algorithm for the finite difference
method in solving the Bratu and Bratu-Type problem 118
E The relative errors of the four methods in
solving the Bratu and Bratu-Type problems 120
CHAPTER 1
INTRODUCTION
1.1 Motivation
\I\Then mathematical modeling is used to describe physical, biological or
chemical phenomena, one of the most common results of the modeling process is
a system of partial differential equations.
The Bratu problem is a partial differential equation which appears 1Il a
number of applications such as the steady state model of the solid fuel ignition
in thermal combustion theory and the Chandrasekhar model of the expansion of
the universe. The former model stimulates a thermal reaction process in a rigid
material, where the process depends on a balance between chemically generated
heat addition and heat transfer by conduction (Averick et al., 1992).
The classical Bratu problem can be described as follows:
o on D: {(x, Y) EO::; x ::; 1 , 0 ::; y ::; I} (1.1 )
with
11 - 0 on 3D,
where 6. is the Laplace operator and D is a bounded domain in TI2. According to
Jacobsen and Schmitt (2001), equation (1.1) arises in the study of the quasi linear
parabolic problem :
(1.2)
l/ 0, x E EJD,
which is also known as the solid fuel ignition model and is derived as a model for
the thermal reaction process in a combustible, nondeformable material of constant
density during the ignition period. Here A is known as the Fmnk-J(amendskii
1 parameter, l/ is a dimensionless temperature and - is the activation energy.
E
The derivation of equation (1.2) from general principles is accounted in the
comprehensive work by Frank and Kamenetskii in year 1955, who are interested
in what happens when combustible medium is placed in a vessel whose walls are
maintained at a fixed temperature. Intuitively, they expected that for a large
value of A, the reaction term will dominate and drive the temperature to infinity
(explosion) whereas for smaller /\ , the steady state might be possible.
Boyd (1986) developed a pseudo spectral method to generate approxiIllate
solutions to the classical two-dimensional planar Bratu problem
( 1.3)
on
{(x,y) E -1:S x:S 1, -1:S y:S I},
with lL = 0 on the boundary of the square. The basic idea is that the uJlkJlO\\"ll
solution u(x, y) can be completely represented as an infinite series of Sj)('ct ml
3
basis functions
N
u(x,y) L ak¢k(X, V)· (1.4 ) k=l
The basis functions ¢k(X, y) are chosen so that they obey the boundary condit.ions
and have the property that the more terms of the series are kept, the more
accurate the representation of the solution u(x, y) is. In other words, as N ~
00 the error diminishes to zero. For finite N, the series expansion in (1.4) is
substituted into (1.3) to produce the residual R. The residual function will depend
on the spatial variables x, y, the unknown coefficients ak and the parameter /\.
The goal of Boyd's pseudo spectral method is to find ak so that the residual
function R is zero at N collocation points. The collocation points are usually
chosen to be the roots of orthogonal polynomials that fall into the same family
as the basis functions ¢k(X, V). Boyd (1986) uses the Gegenbauer polynomials
to define the collocation points. The Gegenbauer polynomials are orthogonal on
the interval [-1,1] with respect to the weight nmction w(x) = (1 - X2)b where
b = - ~ corresponds to the Chebyshev polynomials and b = 1 is the choice Boyd 2
(1986) uses. The second order Gegenbauer polynomial is
3 2 -(5x - 1) 2' , -1 ~ x ~ 1.
Using a I-point collocation method at the point Xl = (1 _1_) and the choice v'5'v'5 of ¢1(X,y) = (1 - x2)(1 - y2), Boyd is able to obtain an approximation to the
value of /\c with a relative error of 8%. Note that this choice for 0] (x, y) satisfies
the boundary conditions since ¢(1, y) = ¢( -1, y) = 0(X, -1) = 0(X, 1) = O. The
solution produced by Boyd's pseudo spectral does not have the deficiency of being
wlable Lo converge to both solutions of the Bratu problem for /\ < /\c.
The Bratu problem in one-dimensional planar coordinates is also of tell
used as a benchmarking tool for numerical methods. The one-dimensional of this
problem is
ul/(X) + Aeu(x) O,O:S;x:S;l, (l.5)
with the boundary conditions
u(O) 0 and u(l) = o.
The nonlinear eigenvalue problem (1.5) has two known bifurcated exact solutions
for values of A < Ac, no solutions for A > Ac and a unique solution when /\ = /\,
where Ac = 3.513830719 is denoted as the critical value (Buckmire, 2003).
In Aregbesola (1996), the method of weighted residuals was used to solve
the Bratu problem (l.5). The idea is to approximate the solution with a polyno-
mial involving a set of parameters. The polynomial is of the form
N
V(x) = <I>o(x) + L A;<I>i(X), i=l
where <I>o(x) satisfies the given boundary conditions and each <I>i(X) satisfies the
homogenous form of the boundary conditions. The function V(x) is then used as
an approximation to the exact solution in the equation
L(U(x)) Q(x)
to give
R(x) L(U(x)) - Q(x).
where the function R(x) is the residual. The alIn is to make R(x) as small
as possible. One of the methods of minimizing R(x) is the collocation method
.5
where R(x) is set to zero at some points in the interval. The system of the
resulting nonlinear equations is then solved to determine the parameters Ai. The
polynomial V(x) is then considered as the approximate solution. The weighted
residual method provides accurate results and was found suitable for bifurcation
problems.
The availability of the exact solution of the Bratu problem (1.5) together
with universal applicability of the standard finite difference method, provides
an important application of the nonstandard finite difference method. Solving
a boundary value problem using the standard and nonstandard finite difFerence
methods involve replacing each of the derivatives by an appropriate difference-
quotient approximation. The interval [a, bJ is divided into N equal subintervals
where
a = Xo < Xl < X2 < ... < Xj < ... < XN = b.
1 For a uniform subintervals, the step size h is constant and h = N with Xi = a+ih
for i = 0,1,2, ... , N. The approximation of the second derivative by using the
centered-difference formula is
(1.6)
However in the nonstandard finite difference method, the denominator of (1.6),
11,2 is replaced by the denominator function ¢(h). Therefore, the nonstandard
fmite difference method for the second derivative is
" 11i+l - 211i + 11i-1 11 ~ ¢(h) (1. 7)
where the denominator function ¢(h) has the property that ¢(h) = h2 + 0(h2).
Buckmire (2003) has employed the standard finite difference method and the
6
nonstandard finite difference method for solving the Bratu problem (1.5). Using
the standard finite difference method, the discrete version of the Bratu problem
(1.5) is
U'i+l - 2U'i + Ui-l \ Ui - 0 h2 + /\e - , i = 1,2, ... ,N - 1. (1.8)
The nonstandard finite difference method for solving the Bratu problem (1.5) is
Ui+l - 2Ui + Ui-l A U
21n[cosh(h)] + e' = 0, i = 1,2, ... ,N - 1, (1.9)
where the denominator function, ¢(h) = 21n[cosh(h)] = h2 + O(h2). Thus, ill the
limit as h --+ 0, the standard finite difference method (1.8) and the nonstandard
finite difference method (1.9) will be identical.
Buckmire extended his research in the application of nonstandard finite
difference scheme to the cylindrical Bratu-Gelfand problem. The cylindrical
Bratu-Gelfand is a particular boundary value problem related to the classical
Bratu problem (1.1), with cylindrical radial operator. Jacobsen and Schmitt
(2002) considered the nature of solutions to a version of the classical Bratu prob-
lem (1.1) generalized to more complicated operators in more dimensions that
they called the Liouville-Bratu-Gelfand problem. The Liouville-Bratu-Gelfand
problem for the class of quasilinear elliptic equations is defined by
0, 0 < T < 1,
U > 0, (1.10)
1[.'(0) = u(l) 0,
7
where the inequalities a ::; 0, 1+ 1 > 0: and (3 + 1 > 0 hold. The Bratu-Gelfand
problem to be considered by Buckmire (2003) is the special case when 0: = 1,
(3 = 0, 1=1 :
1 ( ')' ,11 - ru + /\e r 0, 0 < r < 1,
u > 0,
u'(O) u(l) o.
(1.11)
The assumption has been made that u = u(r) in order to the other derivatives in
Laplacian can be ignored. In his previous works (Buckmire (1996) and (2003)),
he has shown that the usefulness in applying a particular nonstandard finite
difference scheme to boundary value problems in cylindrical coordinates that
contain the expression of r (~~). The expression r (~~) is then approximated by
the forward difference formula,
du Uk+l - Uk r-~rk----
dr rk+l - rk (1.12)
However, the following nonstandard finite difference scheme has been shown
(Buckmire, 2003) to be a superior method, especially for singular problems where
r --t 0:
(1.13)
Using the approximation in (1.12), the Bratu-Gelfand problem (1.11) will be
(1.14)
The nonstandard version finite difference scheme (1.13) for problem (1.11) will
be
o. (1.15)